In the construction and design of air handling fans of the bladed type, the characteristics of the blade must be closely matched to the associated electric motor if optimum efficiency is to be attained. The diameter of the fan blades, their number, the pitch and configuration of the blades', rate of rotation, and other factors determine the "load" produced by the fan during operation, and if the fan motor is undersized for the load produced the motor will overheat and prematurely fail. Conversely, if the motor is larger than required, energy is wasted and the cost of manufacture unnecessarily increased.
The manufacturer of a wide variety of fans for various purposes must custom design each fan size for each purpose and capacity of air flow, and endeavor to obtain an electric drive motor which is most suitable for that particular fan. Often, a larger size motor than optimum must be purchased because of the unavailability of the proper size motor, and a large inventory of blade forming tools must be manufactured as each blade size will require its own special forming tools.
Basically, an air handling fan consists of a hub from which a plurality of blades radially extend. The hub and blades may be homogeneous wherein the entire blade is formed by a casting or molding operation using metal or synthetic material. Larger sizes of fans employ steel hubs and blades wherein the blades are separately affixed to the hubs.
In the conventional assembly of metal hubs and blades, a wide variety of interrelationships between the hub and blades may exist. For instance, the hub may include radially extending stubs which are twisted with respect to the plane of the hub and the blades are affixed thereto by rivets, or the like. Another means for attaching blades to a hub may be to angularly configure the inner end of the blade and directly affix the blade to the hub front side by rivets. In such instance, the blade pitch being determined by the angular relationship of the blade inner end to the hub.
Conventional systems for affixing blades to hubs require special tooling for each blade assembly and the necessary investment in tooling limits the size and capacity of fans offered by a given manufacturer, and as mentioned above, renders it difficult to provide an optimum match between the drive motor and blade assembly.
It is an object of the invention to provide a fan blade fabrication system wherein a variety of blade sizes can be formed from a set of standard tools thereby significantly reducing the tooling investment with respect to known fan fabrication techniques.
Another object of the invention is to provide a fan blade fabrication system which is of low cost and permits the physical characteristics of the fan to be very accurately predetermined permitting the optimum matching with an electric drive motor for achieving the highest efficiencies for moving air with respect to energy consumption.
Another object of the invention is to provide a fan blade fabrication system utilizing a standard set of tools wherein the characteristics of the fan can be predetermined and accurately duplicated, and wherein the fan characteristics may be accurately predetermined.
In the practice of the invention, a flat hub plate is employed having a hub boss affixed thereto whereby the hub may be mounted upon an electric motor shaft. The hub plate includes a plurality of generally radially oriented notches which have been pierced from the plate and intersect the plate circular periphery. Also, a plurality of rivet receiving holes are formed in the plate adjacent the notches for receiving the rivets used to attach the blades thereto.
The blades are formed of sheet metal and the blanks punched from flat stock. The blade blanks are placed within dies which impart a concave-convex configuration to the blade throughout its length, and the blade is of an elongated configuration including an outer end region and an inner end region to be attached to the hub plate. The blade inner end region includes a hub connection portion homogeneously defined of the blade sheet material and of a configuration distinctive from the blade's general transverse cross-sectional arcuate form.
The blade hub connection portion is of an elongated configuration and intersects the blade inner end and is parallel to the blade length. The hub connection portion includes a pair of elongated flat lands or sections which are angularly related to the general form of the blade and are parallel, but offset, with respect to each other and interconnected by an elongated transition portion transversely disposed to the lands. The extent of the offset corresponds to the thickness of the hub plate. When assembling the blade to the hub plate, the transition portion is received within a hub plate notch and one of the lands is located on one side of the hub plate, while the other land is located on the other hub plate side. Rivets extending through the lands and hub plate affix the blade and hub plate in assembled relation.
The angular relationship of the lands to the general blade configuration will be determined by the particular forming tools used, and by using three or four sets of tools having different land angles, a wide variety of fan characteristics can be achieved. Within a given set of tools the positioning of the blade blank therein will locate the hub connection portion as desired relative to the blade longitudinal axis, and by varying the location of the hub connection portion to the blade axis, the physical characteristics of the fan blade assembly can be changed as the projected width of the blades will vary as this dimension is regulated. Accordingly, a single set of tools may be used with a plurality of blade widths and lengths, and in addition to the change in blade characteristics by these factors, the positioning of the hub connection land surfaces on the blade inner end likewise will vary the blade operating characteristics.
As the reception of the blade transition portion within the hub plate notch tends to accurately orient the blade to the hub plate, and as the flat lands firmly engage the flat surfaces of the hub plate, a firm interconnection between the blades and the hub plate is achieved assuring consistent assembling and maximum strength. As the components of the blade assembly are economically manufactured, costs are reduced, and because of the versatility of determining the blade operating characteristics, the assembled blades may be closely matched with available electric motors produced at high production and low cost.